[英]what is wrong with c++ streams when using boost.python?
Update 2: I'm not sure why this is still being upvoted (March 2014). 更新2:我不确定为什么仍要对此进行投票(2014年3月)。 This appears to be fixed since I asked this question many years ago.
自从我多年前问这个问题以来,这似乎是固定的。 Make sure you're using a recent version of boost.
确保您使用的是Boost的最新版本。
UPDATE: Perhaps C++ streams need to be initialized in order to format numbers, and the initialization is not happening when the shared library is loaded in Python? 更新:也许需要对C ++流进行初始化才能格式化数字,并且在Python中加载共享库时初始化没有发生吗?
I am calling 我在打电话
cout << 1 << "!" << endl;
in a method that is exported to a shared library via boost.python. 通过boost.python导出到共享库的方法中。 It doesn't print anything, but if I do
它什么也不会打印,但是如果我打印
cout << "%" << "!" << endl;
it works. 有用。
This is important because I want to do this: 这很重要,因为我想这样做:
ostream& operator <<(ostream &os, const Bernoulli& b) {
ostringstream oss;
oss << b.p() * 100.0 << "%";
return os << oss.str();
}
I exposed that by doing this: 我这样做是暴露了这一点:
BOOST_PYTHON_MODULE(libdistributions)
{
class_<Bernoulli>("Bernoulli")
.def(init<>())
.def(init<double>())
.def("p", &Bernoulli::p)
.def("set_p", &Bernoulli::set_p)
.def("not_p", &Bernoulli::not_p)
.def("Entropy", &Bernoulli::Entropy)
.def("KL", &Bernoulli::KL)
.def(self_ns::str(self))
;
}
but when I call the str
method in python on a Bernoulli object, I get nothing. 但是当我在Bernoulli对象上的python中调用
str
方法时,什么也没得到。 I suspect the simpler cout problem is related. 我怀疑较简单的cout问题是相关的。
I also run into this problem a while ago, using self_ns as outlined in the answers here Build problems when adding `__str__` method to Boost Python C++ class 不久前,我也遇到了这个问题,使用了self_ns,如此处的答案中所述。在向Boost Python C ++类添加`__str__`方法时生成问题
The reason for using self_ns is explained by Dave himself here http://mail.python.org/pipermail/cplusplus-sig/2004-February/006496.html Dave自己在此处解释了使用self_ns的原因,网址为http://mail.python.org/pipermail/cplusplus-sig/2004-February/006496.html
Just for the sake of debugging, please try 只是为了调试,请尝试
inline std::string toString(const Bernoulli& b)
{
std::ostringstream s;
s << b;
return s.str();
}
And replace .def(self_ns::str(self))
with 并将
.def(self_ns::str(self))
替换为
class_<Bernoulli>("Bernoulli")
[...]
.def("__str__", &toString)
Have you tried using boost::format
instead? 您是否尝试过使用
boost::format
? Since you are already using boost
, it shouldn't be too much of a hassle. 由于您已经在使用
boost
,所以它不会太麻烦。
boost::format( "%d%%" ) % ( b.p() * 100.0 )
Another thing, try passing std::endl
explicitly to the output os
. 另一件事,请尝试将
std::endl
显式传递给输出os
。
在使用.str()方法之前,您是否尝试过刷新流?
oss << b.p() * 100.0 << "%" << std::flush;
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